Some large-sized bridges having extremely large spans generally include subsea tunnel sections. A subsea tunnel is formed by connecting a plurality of immersed tubes. Besides the several immersed tubes, the subsea tunnel mentioned in the present application also includes a “sandwich immersed tube structure” capable of being simultaneously connected with immersed tubes on two sides at two final immersed tube jointing portions (the “sandwich immersed tube structure” is also called a final joint which is also an immersed tube, namely a section of a relatively special immersed tube, and after this section of immersed tube is connected with the immersed tubes at its two ends, the subsea tunnel is through).
Corresponding gravel mattresses are disposed on a subsea geologic structure of an installation position of the immersed tubes (including the “sandwich immersed tube structure”). A clearance is reserved between adjacent gravel mattresses, thus forming a furrow. In addition, due to a paving process of the gravel mattresses (an S-shaped trend, as shown in FIG. 4), besides the large furrow formed by the clearance between two gravel mattresses below an immersed tube joint, a plurality of small furrows smaller than the large furrows are also disposed at the top of each gravel mattress.
Specifically, in case of no furrows, when the immersed tubes (including the “sandwich immersed tube structure”) are descended and placed on the gravel mattresses, pressure generated thereby would press the gravel mattresses, the pressed gravel mattresses below immersed tube joints would upwards move to a water stop band, and if the pressure is extremely high, gravels in the gravel mattresses may possibly break through the water stop band; therefore, a furrow structure is disposed.
However, the furrow structure is defective. In an installation process of the immersed tubes (including the “sandwich immersed tube structure”), under the pressure, the gravel mattresses or a geologic structure thereunder may be possibly settled (for example, one of the reasons is that after locked backfilling, if the gravel mattresses are pressed, part of the gravels may possibly move into the furrows, which leads to thinning of gravel mattresses at other positions, thereby resulting in settlement), and at this time, installation postures and heights of the immersed tubes (including the “sandwich immersed tube structure”) do not accord with the standard: the structure itself is tilted or a height deviation (relatively low) occurs relative to an ideal installation position, thus the installation postures and heights need to be readjusted, but the adjustment is relatively difficult, and may affect the progress and the effect of installation; particularly for the final joint, its two ends need to be simultaneously connected with the end portions of two immersed tubes, thus a very high installation requirement is required; if a support at the bottom of the final joint is settled during installation, it is really hard to adjust the installation posture by a conventional adjustment mode (such as hoisting), the efficiency is extremely low, and an adjustment effect is not ideal.
Then, after the immersed tubes (including the “sandwich immersed tube structure”) are installed, the gravel mattresses may be possibly settled due to environmental influence in the sea, and at this time, force, which is originally shared by the gravel mattresses, on the immersed tubes (including the “sandwich immersed tube structure”) at the settled positions is applied to adjacent immersed tube wall bodies through connection members; and under the condition that adjacent immersed tubes have already borne part of force supporting the immersed tubes (including the “sandwich immersed tube structure”), such force transferring may possibly damage connection positions of the immersed tubes and the adjacent immersed tubes (including connection positions of the “sandwich immersed tube structure” and the adjacent immersed tubes), affect the stabilities and the service lives of joints of the immersed tubes (including the “sandwich immersed tube structure”), and then cause a potential safety hazard.
In addition, after the immersed tubes (including the “sandwich immersed tube structure”) are installed, the gravel mattresses do not apply prestress or apply relatively low prestress to the support of the immersed tubes (including the “sandwich immersed tube structure”), and the immersed tubes (including the “sandwich immersed tube structure”) has a poor bearing effect on a load (vehicles and part of external forces) during use.